L-5-hydroxy-tryptophan is a known compound possessing utility in the symptomatic treatment of neurotic and psychotic disturbances wherein the depressive syndrome is manifest. The compound has also been found to possess sedative activity and is therefore also useful in relieving insomnia. L-5-hydroxy-tryptophan however, to be effective in alleviating the symptoms of mental depression must be administered in high dosages, i.e., up to 3 grams or more daily. Such high dosages of L-5-hydroxy-tryptophan have given rise to various undesirable side effects such as, for example, high blood pressure and gastrointestinal complaints which can become sufficiently serious so as to force discontinuance of the medication. It is therefore readily apparent that it would be advantageous to provide a means whereby the dosage of L-5-hydroxy-tryptophan required to achieve the desired therapeutic effect could be materially reduced. Such a reduction in dose would also reduce the undesirable side effects often associated with present dosage levels. Such means are provided in accordance with the present invention by the discovery of synergistic compositions whereby the desired therapeutic effect of L-5-hydroxy-tryptophan can be obtained with a materially reduced dosage. Further, the compositions of the present invention facilitate the therapeutic utilisation of L-5-hydroxy-tryptophan while substantially eliminating the undesirable side effects associated therewith.